/Engine/Source/Runtime/Engine/Classes/Engine/StaticMesh.h
SourceStaticMesh - The data we want to use to add or modify the specified lod  LodIndex - The lod index we want to add or modify.  SourceDataFilename - The source filename thta need to set into the LOD to allow re-import.
bool SetCustomLOD ( const [UStaticMesh](API\Runtime\Engine\Engine\UStaticMesh) * SourceStaticMesh, int32 LodIndex, const [FString](API\Runtime\Core\Containers\FString) & SourceDataFilename )